A habitable Planet...

[Realitycheck]

After looking around a bit more, I just ran into the Drake equation, though I am kind of curious about how the equation is derived, since I plugged in these really generous numbers and it spat out only 13 communicating civilizations per galaxy. Apparently, there are different versions of the equation, as well.

[SkepticLance]

If the Drake equation were written today, it would not be the same equation, since we have learned in the interim period that there are environmental qualities for life that were not really mentioned in the first one. For example ; there is a lot of indication that plate tectonics is needed, and that is not found in all planets.

 

The fact that SETI has found no sign of intelligence, in spite of having scanned over two thirds of our galaxy, is a strong clue that the number of civilisations is not great.

[Realitycheck]

After digging up some more relevant facts, I refined my numbers.

 

About half of our stars are part of binary systems, pretty much ruling them out.

 

Only 25% of these are appropriate for evolving life (live long enough, live stable lives).

 

We'll say that 80% of these have terrestrial planets.

 

Only 1 per 10 stars is located within a temperate range suitable for life, being conservative.

 

.0001 of these have chemical make-up similar enough to earth, again being conservative.

 

This gives you 400,000 planets.

 

Ok, we'll say that only .001 of these planets have an internal heat source with accompanying plate tectonics.

 

400 planets

 

At this point, the equation starts asking you to dictate unknowable facts rather than make reasonable assumptions. One should be able to deduce the average chemical make-up of planets and the odds of one being comprised similar to earth, since there are only a certain number of gases available to make up the atmosphere and most of the metals making up any planet are fairly innocuous. It is pretty hard to determine if life evolves into intelligent life, though a case can be made that it normally does only if the habitat is not an extreme.

 

2/3 of the galaxywas scanned? I thought it was only a small fraction of the galaxy (800 stars, then another 1,000 stars), as Martin pointed out from here.

 

In 1992, the U.S. government funded an operational SETI program, in the form of the NASA "Microwave Observing Program (MOP)". MOP was planned as a long-term effort, performing a "Targeted Search" of 800 specific nearby stars, along with a general "Sky Survey" to scan the sky. MOP was to be performed by radio dishes associated with the NASA Deep Space Network, as well as a 43-meter dish at Green Bank and the big Arecibo dish. The signals were to be analyzed by spectrum analyzers, each with a capacity of 15 million channels. These spectrum analyzers could be ganged to obtain greater capacity. Those used in the Targeted Search had a bandwidth of 1 hertz per channel, while those used in the Sky Survey had a bandwidth of 30 hertz per channel.

 

MOP drew the attention of the U.S. Congress, where the program was strongly ridiculed, and was canceled a year after its start. SETI advocates did not give up, and in 1995 the nonprofit SETI Institute of Mountain View, California, resurrected the work under the name of Project "Phoenix", backed by private sources of funding. Project Phoenix, under the direction of Dr. Jill Tarter, previously Project Scientist for the NASA project, is a continuation of the Targeted Search program, studying roughly 1,000 nearby Sun-like stars. Seth Shostak also worked on Project Phoenix. From 1995 through March 2004, Phoenix conducted observing campaigns at the 64-meter Parkes radio telescope in Australia, the 140 Foot Telescope of the National Radio Astronomy Observatory in West Virginia, USA, and the Arecibo Observatory in Puerto Rico. The project observed the equivalent of 800 stars over the available channels in the frequency range from 1200 to 3000 MHz. The search was sensitive enough to pick up transmitters with 1 GW EIRP to a distance of about 200 light years. (A typical airport radar has this much peak power, but is only on about 1/1000 of the time, and would not have been detected in this survey.)

http://en.wikipedia.org/wiki/SETI

[SkepticLance]

agendchange said

 

"2/3 of the galaxywas scanned? I thought it was only a small fraction of the galaxy"

 

This depends on what you mean by 'scanned'. We could end up in a semantics argument. Obviously, there has not been a detailed scan of two thirds of the stars in the galaxy. However, two thirds of the galaxy area (or more by now) has been roughly scanned - checking for radio signals over large areas of the sky.

 

There are lots of arguments to say that this means very little, and lots of people will push those arguments. For example : advanced civilisations may not use the radio frequencies we scan for. It has been suggested that those civilisations are mor elikely to use directed laser signals.

 

Perhaps that is true. We simply do not have enough data. However, in my own very humble opinion, if there are a large number of civilisations, some should still be at the stage of using radio communication. The fact that we have detected no such signal does not mean no civilisations. However, it probably puts a limit on the number of possible civilisations. Perhaps fewer than 100????

[Mr Skeptic]

Consider that we have only been using radio for a very short time, and the socio-economic situation by that time (in our case, if not in general) allows for very rapid technological progress. Perhaps radio will be completely replaced in one or two hundred years. It could easily be that even with thousands of civilizations, we might be the only ones using radio. Odds are, some civilizations, eg an aquatic civilization, might never use radio at all.

[hmmrn]

Earth might just be unique in our galaxy. Perhaps it's the only habitable planet for humans in the entire milky way. Though there are probably a whole lot of planets like earth throughout universe.

[Ptolemy]

The problem with "Drake" is that it does not take account of factors that appear to be crucial for life on Earth to evolve into complex forms.

These are the strong magnetic field allowing our atmosphere to have lasted long enough and the interaction of our large moon which acts as a brake on the earth rotational spin rate.

It is now probable that the earth and moon was formed by a head on collision of two smaller planets.

This means the original mass of "earth" was significantly lower, ie earth and moon mass minus the mass of collision planet.

The question is what effect this has had?

Would the plant geology be different?,the collision is likely to have allowed heavier elements to have been redistributed nearer the surface, significantly increased mass and makeup of core and formed a relatively large and close moon. The moons relative gravity to earth is considered important in early life development.

The question is how unique is this event in the universe when added to other factors in reducing likelihood of similar complex life coming into existence?

[Moontanman]

The problem with "Drake" is that it does not take account of factors that appear to be crucial for life on Earth to evolve into complex forms.

These are the strong magnetic field allowing our atmosphere to have lasted long enough and the interaction of our large moon which acts as a brake on the earth rotational spin rate.

It is now probable that the earth and moon was formed by a head on collision of two smaller planets.

This means the original mass of "earth" was significantly lower, ie earth and moon mass minus the mass of collision planet.

The question is what effect this has had?

Would the plant geology be different?,the collision is likely to have allowed heavier elements to have been redistributed nearer the surface, significantly increased mass and makeup of core and formed a relatively large and close moon. The moons relative gravity to earth is considered important in early life development.

The question is how unique is this event in the universe when added to other factors in reducing likelihood of similar complex life coming into existence?

 

 

I think there is an argument to be made that with out the moon forming impact the earth would have been a water world with no land surface....

[michel123456]

At the end it may be much more terrifying to realize that we are alone.

[Ptolemy]

I think there is an argument to be made that with out the moon forming impact the earth would have been a water world with no land surface....

This may indeed have been the case,however, the mass and makeup of the original earth may not have had the size and energy in its core to sustain an atmosphere resulting in a temperature and radiation exposure that would have boiled the water away leaving earth in a Mars like state.

[Robittybob1]

 

 

I think there is an argument to be made that with out the moon forming impact the earth would have been a water world with no land surface....

How does that argument go?

[Ophiolite]

This may indeed have been the case,however, the mass and makeup of the original earth may not have had the size and energy in its core to sustain an atmosphere resulting in a temperature and radiation exposure that would have boiled the water away leaving earth in a Mars like state.

I don't follow your logic here. The proto-Earth had a mass not dissimilar to that of today's Earth. The gain in mass following the collision with Theia was minimal. Had the proto-Earth remained with its mass that would have been entirely sufficient to retain an atmosphere.

 

As a secondary point I'm not sure what you mean by the core energy contributing to sustaining the atmosphere.

 

Perhaps you could clarify both points.

[Moontanman]

How does that argument go?

 

It's been awhile since I read it but it assumes an earth mass planet would necessarily have a large amount of water and atmospheric gases, Venus lost it's water to it's greenhouse effect and Mars of course was stripped of it's atmosphere by the solar wind.

 

This idea night have originated in the book "Rare Earth" by Ward and Brownlee

 

https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

 

A planet that is too small cannot hold much of an atmosphere. Hence the surface temperature becomes more variable and the average temperature drops. Substantial and long-lasting oceans become impossible. A small planet will also tend to have a rough surface, with large mountains and deep canyons. The core will cool faster, and plate tectonics will either not last as long as they would on a larger planet or may not occur at all. A planet that is too large will retain too much of its atmosphere and will be like Venus. Venus is similar in size and mass to Earth, but has a surface atmosphere pressure that is 92 times that of Earth's. Venus mean surface temperature is 735 K (462 °C; 863 °F) making Venus the hottest planet in the Solar System. Earth had a similar early atmosphere to Venus, but lost it in the giant impact event.^[23]

[Jandrew]

Mathematically, there has to be. Whether they're intelligent like us, I have no idea, but there just has to be another planet something with some kind of life.

[zapatos]

Mathematically, there has to be. Whether they're intelligent like us, I have no idea, but there just has to be another planet something with some kind of life.

I think it would be helpful if you showed us that math.

[Robittybob1]

 

It's been awhile since I read it but it assumes an earth mass planet would necessarily have a large amount of water and atmospheric gases, Venus lost it's water to it's greenhouse effect and Mars of course was stripped of it's atmosphere by the solar wind.

 

This idea night have originated in the book "Rare Earth" by Ward and Brownlee

 

https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

 

I have no problem accepting an alternate possible water world Earth but it has not been supported by many scientists as yet.

That article didn't really support your argument either.

I am a Moon capture advocate rather than a person supporting the Giant Impact theory for Moon formation. For a Moon capture we would need a Water World Earth to slow the Moon down, that is why I was interested in seeing your arguments for an Earth like that.

Edited February 1, 2016 by Robittybob1

[Moontanman]

I have no problem accepting an alternate possible water world Earth but it has not been supported by many scientists as yet.

That article didn't really support your argument either.

I am a Moon capture advocate rather than a person supporting the Giant Impact theory for Moon formation. For a Moon capture we would need a Water World Earth to slow the Moon down, that is why I was interested in seeing your arguments for an Earth like that.

 

I am not asserting the water world idea is true, i am pretty sure Ward and Brownlee spoke of it in their book Rare Earth. Moon capture hypothesis is not supported by the evidence we have either.

 

Some of the exoplanets that have been found are almost certainly water worlds or mini neptunes due to their size and density and yes some of them are in the habitable zone of their home stars or even closer.

 

Water is the second most common molecule in our universe, nearly all our planets and moons are covered with water ice and other ices to depths of up to thousands of miles. Only Jupiter and Saturn and the inner planets of our solar system do not follow this pattern and we do know of water worlds that are close to their suns in other planetary systems.

 

If I get the chance today I'll dig up my copy of Rare Earth and see if that is where I read of it...

[Ptolemy]

I don't follow your logic here. The proto-Earth had a mass not dissimilar to that of today's Earth. The gain in mass following the collision with Theia was minimal. Had the proto-Earth remained with its mass that would have been entirely sufficient to retain an atmosphere.

 

As a secondary point I'm not sure what you mean by the core energy contributing to sustaining the atmosphere.

 

Perhaps you could clarify both points.

Re the "core" energy I mean the energy ,mainly heat,with the core that keeps the magma molten thus providing the magnetic field essential for our atmosphere.

Re the proto earth mass, if the collision with theia was head on, as now thought probable, the matter of both would be largely combined and the majority of ejected matter formed our moon, hence the proposal the earths mass must have increased.

[Moontanman]

Re the "core" energy I mean the energy ,mainly heat,with the core that keeps the magma molten thus providing the magnetic field essential for our atmosphere.

Re the proto earth mass, if the collision with theia was head on, as now thought probable, the matter of both would be largely combined and the majority of ejected matter formed our moon, hence the proposal the earths mass must have increased.

 

 

Yes, assuming a Mars sized Thea and with Mars 15% as massive as the Earth minus the mass of the Moon which is 1.2% the mass of the Earth, the Earth could have gained 13.8% more mass than it had before the collision.

Edited February 1, 2016 by Moontanman

[Ptolemy]

Yes, assuming a Mars sized Thea and with Mars 15% as massive as the Earth minus the mass of the Moon which is 1.2% the mass of the Earth, the Earth could have gained 13.8% more mass than it had before the collision.

 

I agree but some thinking places thea at much greater perhaps as much as a similar mass to earth.

The real question is if and by how much this was a factor in producing a habitable planet, especially the realatively large and close moon.

Your thoughts?

[Ophiolite]

 

 

Yes, assuming a Mars sized Thea and with Mars 15% as massive as the Earth minus the mass of the Moon which is 1.2% the mass of the Earth, the Earth could have gained 13.8% more mass than it had before the collision.

Most models have a substantial mass lost to the system. The net gain in mass is likely less than 10%. The postulated high mass collisions also involve, I think, glancing blows and thus not a conventional accretion event.

[Airbrush]

What do you think the odds are of a Planet being habitable, and how did you reach that conclusion?

 

Super-Earths may be more habitable than our planet. Three quarters of stars in our area are Red Dwarfs. Not a single Red Dwarf star is visible to the naked eye. Red Dwarfs may be much older than our star. Find a Super-Earth in the habitable zone around a Red Dwarf and you have a good chance for intelligent life or at least complex life.

 

Only problem is some Red Dwarfs have terrible flares or CMEs. What affect would these energetic Red Dwarf outbursts have on a Super-Earth in the habitable zone? Also the planets may become tidally locked with the Red Dwarf star.

 

"In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked. This would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other. Such conditions would appear to make it difficult for forms of life similar to those on Earth to evolve. And it appears there is a great problem with the atmosphere of such tidally locked planets: the perpetual night zone would be cold enough to freeze the main gases of their atmospheres, leaving the daylight zone nude and dry. On the other hand, recent theories propose that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet. Alternatively, a moon in orbit around a gas giant may be habitable. It would circumvent the tidal lock problem by becoming tidally locked to its planet. This way there would be a day/night cycle as the moon orbited its primary, and there would be distribution of heat. In addition, red dwarfs emit most of their radiation as infrared light..."

 

https://en.wikipedia.org/wiki/Red_dwarf_star#Habitability

 

 

"According to one theory,^[78] super-Earths of about two Earth masses may in fact be more conducive to life than our own planet. The higher surface gravity would lead to a thicker atmosphere, increased surface erosion and hence a flatter topography. The end result could be an "archipelago planet" of shallow oceans dotted with island chains ideally suited for biodiversity. A more massive planet of two Earth masses would also retain more heat within its interior from its initial formation much longer, sustaining plate tectonics (which is vital for regulating the carbon cycle and hence the climate) for longer. The thicker atmosphere and stronger magnetic field would also shield life on the surface against harmful cosmic rays."

 

https://en.wikipedia.org/wiki/Super-Earths#Habitability

Edited February 4, 2016 by Airbrush

[Ophiolite]

Re the "core" energy I mean the energy ,mainly heat,with the core that keeps the magma molten thus providing the magnetic field essential for our atmosphere.

I don't think I am being pedantic to point out that the core is a molten iron-nickel-minor element mix. It is not a magma. The slightly smaller Earth, without a collision, would still have a molten core and a magnetic field and a retained atmosphere.

 

Re the proto earth mass, if the collision with theia was head on, as now thought probable, the matter of both would be largely combined and the majority of ejected matter formed our moon, hence the proposal the earths mass must have increased.

 

And Theia is generally described as Mars sized. And Mars has 1/10th the mass of the Earth. And some mass was lost in the collision. So any mass increase is minimal and unlikely to have had any major influence on subsequent planetary geology. Can you demonstrate a major influence from theoretical considerations?

[Ptolemy]

Latest research analysing the moon and earth suggests the impact was head on and earth and the moon formed with theia being equally dispersed into both bodies.

This is the only explanation for the formation of such a relatively large moon in such close proximity. Obviously any atmosphere would have had to form after this event.

The question is how critical is the moon to making our planet habitable.

Also this impact is credited with redistributing the heavy metals closer to the surface.

The next question would be how rare are such collisions where the impact is sufficient to cause this effect but no so violent as to obliterate the two bodies, and take place in the Goldilocks zone.

What is not yet known is if this significantly change earths orbit distance

By equally, I meant uniformly

[pavelcherepan]

 

Latest research analysing the moon and earth suggests the impact was head on

 

In their paper they say that the best fit is 32-35^o angle of impact. It's confusing when people keep saying "direct impact". They don't even use this term in the paper.

 

http://arxiv.org/ftp/arxiv/papers/1207/1207.5224.pdf

 

 

Obviously any atmosphere would have had to form after this event.

The question is how critical is the moon to making our planet habitable.

 

There would've been an earlier atmosphere before the impact. And Moon probably is pretty important for development of life, but we can't say for sure, because we don't know any other places with life other than Earth.

Edited February 7, 2016 by pavelcherepan